The airborne transmission of bacteria and viruses, chiefly respiratory disease organisms is a serious problem in health care. The control of airborne disease transmission has become increasingly important with an increasing number of people growing older with weakened immune systems more vulnerable to airborne disease or infected with human immunodeficiency virus (HIV) or other airborne and difficult to cure diseases. This coupled with antibiotic resistant strains of bacteria have created a need for inexpensive, efficient air purification systems. The spread of air born infections can be reduced by killing the infectious microorganism by ultraviolet (UV) radiation. Ultraviolet radiation to destroy airborne microorganisms can be used in ceiling fixtures suspended above the people in the room or inside ventilation system air duct.
The continuing spread of tuberculosis (TB) infection and other airborne disease in modern health institutions, correctional institutions, and shelters for homeless indicates however, that the known air purification systems are inadequate in controlling the spread of airborne microorganisms.
An other important field where the spread of microorganisms needs to be controlled is liquid, and particularly waterbased solutions.
The sterilization by ultraviolet radiation has been known more than fifty years. Various methods and apparatus have been invented for ultraviolet irradiating fluids, air and water in particular, in order to control the spread of microorganisms by destroying those microorganisms with a sufficient dose of radiation.
Air purification by means of filtration and irradiation is widely practiced. Conventional air cleaning systems commonly have a filtration and irradiation units. Irradiation is placed after filtration because the ultraviolet lamps used as a source of the radiation readily attract dust which can accumulate on a surface of the lamp, block the UV radiation inside the lamp and interfere with their germicidal effect.
Commonly irradiation is placed before humidification because ultraviolet radiation is most effective in an atmosphere with relative humidity less than 70% which promotes oxidation. Ultraviolet germicidal radiation has been proven to be more effective and economically feasible than any other approach to reducing the number of microorganisms in the liquid or gas flow.
Conventional UV fluid sterilization systems have relied on exposure of suspended microorganisms to ultraviolet radiation by passing medium over or around one or more ultraviolet lamps. This method is used in U.S. Pat. Nos. 5,112,370 and 5,200,156. This method has a number of shortcomings.
The first shortcoming of the previous art is their low reliability. The particles suspended in the fluid accumulate on the surface of the lamp or protective tubes, forming the UV light absorption layer, which restricts or eliminates the germicidal effectiveness. The reliability and actual germicidal effectiveness depend on the quality of the medium filtration and come very small and unpredicted if the medium is unfiltered or poorly filtered.
The second shortcoming of previous art of UV sterilization systems is that they have low efficiency of use of the UV energy, because their lamps accumulate particles on the surface from the beginning and because in ducts or pipes with ratio length-L to diameter-D L/D=10:1 only 6% of beams have their path length equal to the longest available way (L/2 that is when the lamp is placed halfway between the longest straight line length of the duct (L), the maximum available way is only L/2), other beams, 94% are directed on much shorter paths and could irradiate smaller volume on its way, and, hence, are less efficient.
The third shortcoming of previous art is nonuniform irradiation intensity in an irradiated volume. In the device for sterilization according to U.S. Pat. No. 5,200,156 the author tried to achieve more uniform irradiation intensity than before by applying a flat oval cross section light source with or without the reflectors. But this invention made limited progress because the according to the U.S. Pat. No. 5,200,156 can irradiate towards axis of pipe only 50% of radiation and only 6% of the beams will have length equal to the length of the longest available way. Other beams are short slanting beams. They irradiate smaller volume than longest beams and are absorbed by the pipe walls. Due to the early absorption, the efficiency of the use of short slanting beams is very low. As a result the efficiency of all previous art, including the sterilizer according to U.S. Pat. No. 5,200,156 is too low.
The fourth shortcoming of previous art according to U.S. Pat. No. 5,200,156 is that the sources of radiation are installed inside the medium flow, liquid or gas, and create a substantial pressure loss in the system. To retrofit an operating ventilation or other system with known UV sterilization system it is necessary to replace a fan, pump, electric motor by more powerful equipment.
In U.S. Pat. No. 5,635,133, the above mentioned shortcomings were eliminated by an apparatus invented by Dr. Mark Glazman that increased the efficiency of the germicidal radiation for killing microorganisms by first providing a secondary flow of particle free fluid that maintained the surfaces of the means for transferring and orienting the germicidal beams free of energy absorbing dust particles and by secondarily orienting the germicidal beams of radiation into an array of parallel beams which when passed though a duct containing a primary flow of fluid medium achieved a very high efficiency due to the orientation of the beams being generally parallel to the duct path.
This apparatus utilized an ultraviolet lamp and a substantially parabolic reflector to achieve these improvements in combination with other elements.
A feature of this design was the ability to place the UV lamp at one end of the duct and direct the array of beams along the path of the flow of the primary medium.
While this invention of Dr. Glazman has demonstrated a dramatic increase in germicidal efficiency particularly in the area of air purification in ducted ventilation systems, further developments have been discovered that can increase the efficiency even further.
The first Glazman air purification system relied on a straight portion of ducting to achieve a microorganism killing zone or path. This path was preferably about 3 meters in length, the longer the better.
In many applications, the length available to create a killing path may be substantially less than 3 meters, often 2 meters or less is available in which the germicidal effect must be achieved. The problem is how to efficiently and safely create a highly effective kill zone in a very short duct.
In many applications, both residential and commercial, there simply is no available central ducting to be used. In these situations, the apparatus for killing microorganisms must be capable of providing its own flow path of fluid medium. In these cases, the apparatus may have a very short flow path available in which to kill the microorganisms.
In such a case a self contained device is needed. In U.S. Pat. No. 5,112,370 by Michele Gazzano of Milan, Italy, a Device for Sterilizing a Forced Air Flow by Means of Ultraviolet Radiation, discloses an elongated housing provided with reflecting inner surfaces accumulating an ultraviolet radiation source and a fan for sucking air into the device and sending it out after being subjected to ultraviolet radiation in an air flow passage. The reflective surfaces were formed in an optical labyrinth with a plurality of parallel and spaced sheets defining paths for the air flow and shielding and absorbing the ultraviolet radiation to prevent escaping thereof outside the device.
The Gazzano device as disclosed shows the cylindrical UV lamp's orientation as being parallel to the air flow path. Accordingly the UV beams had to be deflected at an angle of about 150 degrees off of numerous reflective surfaces in order to achieve any meaningful killing zone. The reflective surfaces further included the internal surfaces of the housing which also were perpendicular to the beam paths. The entire length of the killing zone was limited effectively to the length of the UV lamp. To compensate for this shortcoming the Gazzano device employed four parallel lamps this enables the device to become wider and accordingly could accommodate more air. A primary limitation of this device was the requirement that multiple lamps were needed. It is readily appreciated that the apparent effective kill zone on a per lamp basis was limited to about a distance of 2 to 3 times the diameter of the UV lamps glass envelope. This is an easily recognized limitation of the use of lamps wherein the beam is directed perpendicular to the air flow.
In the present invention it is an objective to use an Ultra violet lamp as a means for killing microorganisms, hereinafter referred to as a source of germicidal beams.
It is a further objective to provide an apparatus, which includes the ultra violet lamp, the apparatus providing a way in which the germicidal beams are more efficiently used in a very short length of a germicidal killing zone.
It is a further objective that the apparatus substantially blocks the escape of all the radiation emitted by the UV lamp.
It is a further objective to maintain the orientation of UV lamp so that the beams are directed substantially along the same direction as the fluid medium path.
It is a further objective of the invention that the device can achieve an efficient kill rate with as few as one UV lamp.
It is still a further objective that the apparatus be fully self contained only requiring an electrical connection to provide power to the UV lamp, its ballast and any fans and motors if used to provide an air flow.